Question

What should be the volume of milk (in ${m^3}$) which measures $5L$?
A: $5 \times {10^{ - 3}}{m^3}$
B: $5 \times {10^3}{m^3}$
C: $5 \times 1000{m^3}$
D: $5 \times {10^6}{m^3}$

Answer 1

Unit of measurement is a definite magnitude of a quantity that is adopted to define a particular quantity. For example length is a physical quantity and meter is used to define this quantity. Some other units are used to define length but meters are used as standard units. Values may change with the change in units.

Complete step by step answer:
As we know units are used to define quantities. With the help of units we determine what the given quantity is. For example if we say only $5$ it will mean nothing. Like it could be $5L$, $5m$, $5N$, $5Pa$ or $5s$. It could be anything. So it becomes necessary to use units after writing some values. A physical quantity can be defined in more than one unit as well. For example we measure length in $m$, $cm$, $ft$. If we have some material of length $1m$ then it doesn’t mean that it will be equal to $1cm$ or $1ft$. It will have some other value in other units. These values are decided already. For example $1m = 100cm = 3.2ft$
Same happens with other quantities as well. In this question we have given a volume of $5L$ and we have to find a value of $5L$ in ${m^3}$. There is $1000L$ in $1{m^3}$. This means
$1L = {10^{ - 3}}{m^3}$
We have to find a value of $5L$ in ${m^3}$. Therefore;
$5L = 5 \times {10^{ - 3}}{m^3}$ (Multiplying above equation by $5$)
So, correct answer is option A that is $5 \times {10^{ - 3}}{m^3}$.

Note:
There are different systems used to define units. For example: $SI$, $FPS$, $MKS$, $CGS$ etc. $SI$ system is a standard system. This system is preferred worldwide. In $SI$ system there are $7$ primary units. These are meter $\left( m \right)$, kilogram $\left( {Kg} \right)$, second $\left( s \right)$, ampere $\left( A \right)$, candela $\left( {cd} \right)$, mole $\left( {mol} \right)$ and Kelvin $\left( K \right)$.